The present invention relates to a process for producing ultrasonic transducers having complex shapes and is applicable to obtaining annular transducers.
More specifically, the invention relates to a process for producing complex piezoelectric transducers formed from a plurality of elementary transducers which can have varied shapes and obtained by cutting from a piezoelectric ceramic block. These transducers are more particularly used in medical echography processes.
When the elementary transducers are applied to the patient's skin, they transmit ultrasonic waves, which are propagated in the tissues and are reflected on an obstacle or interface. The echos or reflected waves coming from these interfaces reach the transducers used, then serving as receivers, with a time lag compared with transmission and which is dependent on the distance between the transducer and the reflecting surface. When the time required for an outward and return travel has elapsed, a new pulse can be transmitted. The echos can then be displayed on an oscilloscope screen.
Transducers with complex shapes and in particular ring grating transducers using echo tracking focusing are already known. This focusing of the received wave at a point located on the transmitted wave front makes it possible to obtain a good resolving power for two echo points located on the "firing line". Such transducers are described in the article which appeared in Acta Electronica of 22.2.1979, pp. 119 to 127 and entitled "Echo tracking focusing ring grating transducers". Such ring grating or annular transducers are constructed from a plurality of square elementary transducers electrically connected to an electronic switching device making it possible to group said elementary transducers in the form of concentric circles. As these annular transducers do not have a predetermined shape, it is necessary to use an extremely complex switching device, both from the construction and from the operational standpoints.